Thanks Robby ... and I was so close!
The revised and improved version of the slides is up: http://www.slideshare.net/DanielPrager/introduction-to-contracts-and-functional-contracts Cheers Dan On Thu, Sep 5, 2013 at 7:37 AM, Robby Findler <ro...@eecs.northwestern.edu>wrote: > You need to indicate that the contract on 'r' needs 'n', ie replace "[r > (->i" with "[r (n) (->i". > > Robby > > > On Wed, Sep 4, 2013 at 4:33 PM, Daniel Prager > <daniel.a.pra...@gmail.com>wrote: > >> On Wed, Sep 4, 2013 at 7:58 AM, Matthias Felleisen <matth...@ccs.neu.edu> >> wrote: >> >> You can't. Sam has had this combination on his todo list for 7 years and >>> he never got around to it. Perhaps I signed his dissertation too early :-) >> >> >> I noticed that contract support is missing from TR. I have, however, >> constructed a roll-my-own contract example with TR, and it would be great >> if Sam (or another!) pushed forward on contract support for TR. >> >> This is from my code base. It is a function that consumes the dimensions >>> of a (functional image) canvas and created a gridded image and an event >>> handler that tells you on which "tile" a user clicked. It is highly real, >>> higher-order, dependent, and yet not difficult to understand. >> >> >> Alas, I am having trouble mentally parsing this, but may still flash it >> up (with acknowledgement!) as a realistic example. >> >> In trying to construct a simpler (yet not easily do-able with static >> types) example I'm running into trouble getting my subcontract right. >> >> I get an "n unbound identifier" error on the penultimate line: >> >> ;; make-indenter: Nat -> (String -> String) >> ;; >> ;; Example: ((make-indenter 4) "foo") -> " foo" >> ;; >> (define/contract (make-indenter n) >> (->i ([n natural-number/c]) >> [r (->i ([s string?]) >> [result string?] >> #:post (s result) (= (string-length result) >> (+ n (string-length s))))]) >> (λ (s) (string-append (make-string n #\space) s))) >> >> >> How should I access 'n'? >> >> >> Many thanks >> >> Dan >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users >> >> > -- *Daniel Prager* Agile/Lean Coaching, Software Development and Leadership Twitter: @agilejitsu <https://twitter.com/agilejitsu> Blog: agile-jitsu.blogspot.com
____________________ Racket Users list: http://lists.racket-lang.org/users
